Catalysts are well known to be useful in certain reactions. In particular, they can be used to promote particular reactions that would not normally take place in the absence of the catalyst.
A typical catalyst comprises one or more catalytically active components supported on a catalyst support. Typically, the catalytically active components are metals and/or metal-containing compounds. The support materials are generally high surface area materials with specific pore volumes and distribution.
Various methods for depositing catalytically active components on catalyst supports are known. For example, the catalyst support may be impregnated with an aqueous solution of the catalytically active component(s). The impregnated support may then be dried, and calcined. An example of such an impregnation technique is described in WO 01/96017.
The catalytically active component may also be deposited onto the catalyst support by precipitation. In EP 0569624, for example, a catalyst support is first impregnated in an aqueous solution of a noble metal. The metal is then precipitated onto the support by contacting the impregnated support with an aqueous solution of an alkali metal salt.
A further method of depositing a catalytically active component on a catalyst support is the sol-gel method. In the sol-gel method, a metal compound or oxide is hydrolysed in the presence of a stabiliser, such as an amphiphilic betaine, to produce colloidal particles of the metal oxide. The particles may be co-precipitated onto a support formed of gel precursors of, for example, hydrolysed Si(OMe)4. An example of such a process is described in DE 19852547.